Top 65 MongoDB Interview Questions with Answers in 2025

If you are looking for the most asked MongoDB Interview Questions and answers, you are at the right place. MongoDB is a popular NoSQL database known for its flexibility, scalability, and ease of use. Whether you're a MongoDB professional looking to refresh your knowledge or a beginner preparing for job interviews, this blog is equally important for you.  

This blog has been designed to equip you with the essential knowledge needed to confidently tackle any MongoDB interview. In this blog, you will learn about the top 65 most asked MongoDB Interview Questions and their answers. So, continue reading further! 

Table of Contents 

1) Basic MongoDB Interview Questions and answers 

   a)  What is MongoDB? 

   b)  What are the advantages of using MongoDB? 

   c)  How does MongoDB ensure high availability? 

   d)  Explain the concept of sharding in MongoDB. 

   e) What is BSON? 

   f) How can you create a database in MongoDB? 

   g)  How do you insert documents into a collection in MongoDB? 

   h)  What is the difference between findOne() and find()? 

   i) How can you update a document in MongoDB? 

   j)  Explain the Aggregation Pipeline in MongoDB. 

2) Advanced MongoDB Interview Questions and answers

3) Conclusion

Basic MongoDB Interview Questions 

As data volumes and complexity continue to grow, MongoDB's ease of use has made it a good choice for a wide range of applications. From web and mobile apps to real-time analytics and Internet of Things (IoT) devices, MongoDB is a popular NoSQL database.  

Understanding MongoDB's core concepts, features, and best practices is crucial to making the most of this powerful database technology and building strong MongoDB Skills. So, let us begin with MongoDB basic interview questions for beginners. 

1) What is MongoDB? 

MongoDB is a high-performance, open-source, document-oriented NoSQL database that stores data in JSON-like BSON format. It is designed to handle unstructured data and offers dynamic schema capabilities.  

2) What are the advantages of using MongoDB?  

The following are the advantages of using MongoDB: 

a) Flexible and schema-less data model 

b) Horizontal scalability with sharding 

c) High performance due to memory-mapped storage engine 

d) Easy integration with various programming languages 

e) Rich query language support 

3) How does MongoDB ensure high availability?  

MongoDB ensures high availability through replica sets. A replica set consists of multiple nodes, including a primary and a secondary node. If and when the primary node fails, the secondary nodes will be automatically elected as the new primary. 

4) Explain the concept of sharding in MongoDB.  

Sharding is used to distribute data across multiple machines to achieve horizontal scalability. Each shard contains a subset of data, and mongodb sharding ensures efficient data distribution and load balancing across shards with the help of MongoDB's balancer.

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5) What is BSON?  

BSON or Binary JSON is a binary representation of JSON documents used in MongoDB for efficient storage and data exchange.  

6) How can you create a database in MongoDB?  

To create a new database in MongoDB, use the use command followed by the database name. MongoDB creates the database when you insert data into it. 

7) How do you insert documents into a collection in MongoDB?  

You can insert documents into a collection using the insertOne() or insertMany() methods. 

8) What is the difference between findOne() and find()?  

findOne() returns a single document that matches the query, while find() returns a cursor to the documents that match the query. 

findOne() returns null if no document matches the query, while find() returns an empty cursor. 

9) How can you update a document in MongoDB?  

You can update a document using the updateOne() or updateMany() methods. 

10) Explain the Aggregation Pipeline in MongoDB.  

The Aggregation Pipeline is a powerful tool for processing and transforming data in MongoDB. It consists of stages, each representing a data processing step. Documents are passed through the stages in sequence, allowing complex data manipulations. 

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11) What is the use of the $match stage in the Aggregation Pipeline?  

The $match stage filters documents based on a specified condition, similar to the find() method. 

12) How can you index data in MongoDB?  

You can create indexes using the createIndex() method. Indexes improve query performance and help in optimising data retrieval. 

13) What is a covered query in MongoDB?  

A covered query is a type of MongoDB Query where all the queried fields and the fields to return are covered by an index, making the query faster.  

14) Explain the concept of Time-to-Live (TTL) indexes.  

TTL indexes automatically delete documents after a certain period, specified in seconds. 

db.collection.createIndex({ createdAt: 1 }, { expireAfterSeconds: 3600 }) 

15) How do you perform transactions in MongoDB?  

MongoDB supports multi-document transactions for replica sets and sharded clusters using the startSession() and commitTransaction() methods. 

16) What is the use of the $project stage in the Aggregation Pipeline?  

The $project stage allows you to reshape the documents by specifying which fields to include or exclude from the output. 

17) Explain the $group stage in the Aggregation Pipeline.  

The $group stage is used for grouping documents by a specified key and performing aggregate functions on the grouped data. 

18) What is a compound index in MongoDB?  

A compound index includes multiple fields, offering better query performance for complex queries. 

19) How do you perform text search in MongoDB?  

MongoDB supports text search using the $text operator. 

20) Explain the purpose of the $unwind stage in the Aggregation Pipeline.  

The $unwind stage is used to transform an array field into multiple documents, one for each array element. 

21) How can you perform a case-insensitive search in MongoDB?  

You can perform a case-insensitive search using regular expressions with the i option. 

22) What is the use of the $sort stage in the Aggregation Pipeline?  

The $sort stage is used to reorder the documents based on a specified field. 

23) How do you delete documents from a collection in MongoDB?  

You can delete documents using the deleteOne() or deleteMany() methods. 

24) Explain the concept of indexing strategies in MongoDB. 

MongoDB offers various indexing strategies, including single-field indexes, compound indexes, multi-key indexes, and geospatial indexes, to optimise query performance for different use cases.  

25) What is the use of the $limit stage in the Aggregation Pipeline?  

The $limit stage restricts the number of documents passed to the next stage in the Aggregation Pipeline. 

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Advanced MongoDB Interview Questions and answers 

After covering some basic and frequently asked interview questions on MongoDB, here are some advanced-level questions: 

26) How do you perform a bulk write operation in MongoDB?  

You can use the bulkWrite() method to perform multiple insert, update, or delete operations in a single request.  

27) Explain the explain() method in MongoDB.  

The explain() method provides information about how a query is executed, including details about the chosen index, execution time, and more. It helps in query optimisation. 

28) What is the GridFS in MongoDB?  

GridFS is a specification used for storing and retrieving large binary files, such as images or videos, in MongoDB.  

29) How do you create a TTL index for specific documents in MongoDB?  

You can create a TTL index with a filter to apply the expiration only to specific documents. 

30) Explain the concept of capped collections in MongoDB.  

Capped collections are fixed-size collections that automatically overwrite older documents when the collection reaches its maximum size. They are useful for storing logs and other time-sensitive data. 

31) What are indexes in MongoDB, and why are they essential?  

Indexes in MongoDB are data structures that improve the performance of queries by providing efficient access to data. They help speed up data retrieval and reduce the amount of data MongoDB needs to scan to find the matching documents. With MongoDB Find, indexes make queries faster by quickly locating relevant documents.  

32) How do you drop a collection in MongoDB?  

You can drop a collection using the drop() method. 

db.collection.drop() 

33) Explain the concept of a covered query in MongoDB.  

A covered query is a query where all the fields in the query are part of an index, and the index contains all the data needed to fulfil the query. As a result, MongoDB can return the results directly from the index without accessing the actual documents.  

34) How can you perform a case-insensitive sort in MongoDB?  

You can perform a case-insensitive sort using the $collation option.  

35) What is the Aggregation Framework in MongoDB?  

The Aggregation Framework is a powerful tool for processing and transforming data in MongoDB. It consists of pipeline stages that allow complex data manipulations, filtering, grouping, and more.  

36) Explain the purpose of the $group stage in the Aggregation Framework.  

The $group stage groups documents by a specified key and performs aggregate functions on the grouped data.  

37) How do you perform a text search with stemming in MongoDB?  

To perform a text search with stemming, use the $text operator along with the $language option. 

38) What is the primary key in MongoDB, and can it be changed?  

In MongoDB, the primary key is the _id field, and it uniquely identifies each document in a collection. Once set, the _id value is immutable and cannot be changed.  

39) How can you create a compound index with a unique constraint in MongoDB?  

You can create a compound index with a unique constraint by setting the unique option to true. 

40) What are Secondary Indexes in MongoDB?  

Secondary indexes in MongoDB are additional indexes created on fields other than the primary key. They allow for efficient querying on frequently accessed fields.  

41) How can you limit the number of documents returned in a MongoDB query?  

You can use the limit() method to restrict the number of documents returned in a query. 

42) What is the purpose of the $skip stage in the Aggregation Framework?  

The $skip stage is used to skip a specified number of documents in the Aggregation Pipeline. 

43) How do you perform a case-sensitive search in MongoDB?  

To perform a case-sensitive search, use a regular expression without the i option. 

44) Explain the concept of Journaling in MongoDB.  

Journaling in MongoDB is a feature that provides data durability by writing every write operation to a journal before applying it to the database. This ensures that data is not lost in the event of a crash.  

45) How can you retrieve distinct values from a field in MongoDB?  

You can use the distinct() method to retrieve distinct values from a field. 

46) What is the difference between a NoSQL database and a relational database?  

In a NoSQL database like MongoDB, data is stored in a non-tabular, flexible format, usually as JSON-like documents. NoSQL databases are horizontally scalable and better suited for handling unstructured data and large volumes. On the other hand, a relational database follows a tabular structure with predefined schemas and is suitable for structured data with complex relationships between tables.  

47) How does MongoDB handle transactions?  

MongoDB supports multi-document transactions for replica sets and sharded clusters. Transactions provide all-or-nothing semantics, allowing multiple operations to be grouped into a single transaction that either succeeds completely or fails entirely.  

48) What is Map-Reduce in MongoDB?  

Map-Reduce is a data processing paradigm used in MongoDB to perform complex data aggregations and transformations. However, for many cases, MongoDB Aggregate can offer a more streamlined and efficient way to perform these operations. It involves two stages: Map, where data is sorted and grouped based on a key, and Reduce, where the grouped data is aggregated based on the key.

49) How do you perform a case-insensitive text search with stemming in MongoDB?  

To perform a case-insensitive text search with stemming, use the $text operator along with the $caseSensitive and $diacriticSensitive options. 

50) Explain the concept of a database profiler in MongoDB.  

The database profiler is a feature in MongoDB that allows you to record and analyse performance statistics for database operations. It helps in identifying slow queries and potential bottlenecks.
 

 

52) What is the use of the $graphLookup stage in the Aggregation Pipeline?  

The $graphLookup stage performs a recursive search on a collection, allowing you to perform graph-based queries and retrieve connected data.  

53) How do you backup and restore a MongoDB database?  

You can backup a MongoDB database using the mongodump command and restore it using the mongorestore command. 

54) What is the significance of the WiredTiger storage engine in MongoDB?  

WiredTiger is the default storage engine in MongoDB since version 3.2. It offers significant improvements in performance, compression, and concurrency control, making MongoDB more efficient and scalable.  

55) How can you retrieve the total count of documents in a collection in MongoDB?  

You can use the countDocuments() method to retrieve the total count of documents in a collection. 

56) Explain the concept of Change Streams in MongoDB.  

Change Streams in MongoDB allow applications to listen for real-time changes in a collection. They provide a way to monitor data changes and trigger actions based on those changes.  

57) How do you create an index on an array field in MongoDB?  

To create an index on an array field, specify the field name inside quotes in the createIndex() method. 

58) What is the $out stage in the Aggregation Framework used for?  

The $out stage writes the output of an aggregation pipeline to a specified collection, effectively creating a new collection with the aggregated data.  

59) How can you perform a case-insensitive sort with collation in MongoDB 4.0+?  

MongoDB 4.0 introduced collation support directly in the sort() method. 

60) Explain the difference between sharding and replication in MongoDB.  

Sharding is the process of distributing data across multiple servers or shards to achieve horizontal scalability and handle large amounts of data. While replication is the process of synchronising data across multiple servers to ensure high availability and data redundancy. It involves creating multiple copies (replicas) of data on different nodes. 

61) How can you find the size of a collection in MongoDB?  

You can use the stats() method to find the size of a collection in MongoDB. 

db.collection.stats().size 

62) Explain the concept of compound documents in MongoDB.  

Compound documents in MongoDB refer to nested or embedded documents within a document. This allows you to represent complex data structures and relationships without the need for joins as in traditional relational databases.  

63) What is the purpose of the $redact stage in the Aggregation Framework?  

The $redact stage allows you to apply access control rules to restrict the documents returned in the aggregation pipeline based on certain conditions.  

64) How do you perform a full-text search with weights in MongoDB?  

To perform a full-text search with weights, use the $text operator along with the $search option and the $meta projection to specify the weights for fields. 

65) What are TTL indexes, and how do they work in MongoDB?  

TTL (Time-to-Live) indexes in MongoDB are special indexes that automatically remove documents after a specified amount of time. They are commonly used for data that has an expiration date, such as temporary sessions or log entries. 

Conclusion 

With these top 65 essential MongoDB Interview Questions, you now have a more extensive knowledge base to prepare for your MongoDB job interview. Remember to practice and explore MongoDB's features to gain a sound understanding of this powerful NoSQL database.  

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